This can be related to process vessels, hoppers, pits, etc.- just about any “open-topped” space. Now, when it comes to hoppers, these will fall into the PRCS category based solely on their design with “inwardly converging walls or by a floor which slopes downward and tapers to a smaller cross-section.”
But even then, a very shallow hopper does not pose the same hazards by its “inwardly converging walls” as does a hopper that is deeper. And here lies the question… have we defined and quantified when a space would be a “confined space”?
For me, based on OSHA documents and discussions, I have always used…
Four (4) feet deep as my threshold.
This threshold comes out of ANSI standard on Confined Spaces and OSHA’s construction standards on Trenching, which states the following:
| 1926.651(g)(1)(i) Where oxygen deficiency (atmospheres containing less than 19.5 percent oxygen) or a hazardous atmosphere exists or could reasonably be expected to exist, such as in excavations in landfill areas or excavations in areas where hazardous substances are stored nearby, the atmospheres in the excavation shall be tested before employees enter excavations greater than 4 feet (1.22 m) in depth. |
I also like to reference ANSI Z117.1-1977, “Safety Requirements for Working in Tanks and Other Confined Spaces,” in which ANSI used the 4′ depth to quantify the depth that would make a space a CS. The ANSI standard defined confined spaces as enclosures with limited means of access and egress, such as storage tanks, open-topped spaces more than four feet in depth with poor natural ventilation, and sewers.
This LOI from 1995 also discusses these types of spaces. Although it does NOT mention the 4′ aspect of these spaces, you can get the idea that some open-top spaces are indeed CS, and some will be PRCS based on their potential hazards.
